1. Field of the Invention
This invention relates to a method and apparatus for dressing an angular grinding wheel having a first grinding surface usable for grinding a cylindrical surface of a workpiece and a second grinding surface perpendicularly intersecting the first grinding surface and usable for grinding a shoulder end surface of the workpiece.
2. Description of the Background Art
An angular type grinding wheel G has a first grinding surface Ga and a second grinding surface Gb perpendicularly intersecting the first grinding surface Ga, as shown in FIG. 1, so as to simultaneously grind a cylindrical surface and a shoulder end surface of a workpiece.
Conventionally, the first and second grinding surfaces Ga, Gb of the grinding wheel G are dressed using a touch detection device which is provided with an AE sensor (Acoustic Emission Sensor) for detecting the positions of the first and second grinding surfaces Ga, Gb, respectively. Namely, a dressing tool is firstly advanced toward the first grinding surface Ga until the contact between the dressing tool and the first grinding surface is detected by the touch detection device. The dressing tool is then fed into the first grinding surface Ga by a few microns so as to dress the first grinding surface Ga. The second grinding surface Gb is also dressed in the same manner.
In grinding operation, the first and second grinding surfaces Ga, Gb wear down differently, because a cylindrical surface and shoulder end surface of a workpiece have different removal amounts to be ground, respectively and they are ground under different grinding conditions, respectively. Therefore, during grinding operation, the position of top portion Gp of the grinding wheel gradually deviates from the reference plane RP in which the top portion Gp initially lay, as indicated by a broken line L1 in FIG. 1.
Accordingly, when the first and second grinding surfaces Ga, Gb are respectively dressed by predetermined dressing amounts dt and de with the worn first and second grinding surfaces being used as reference positions, the grinding wheel would have a shape indicated by a broken line L2 after such dressing operation. Namely, the position of the top portion Gp has deviated from the reference plane RP toward the second grinding surface Gb by an amount of S.
In grinding operation, the relative position between the grinding wheel G and a workpiece W is controlled under the assumption that the top portion Gp of the grinding wheel G always lies in the reference plane RP. Namely, when both of a cylindrical surface W1 and a shoulder end surface W2 of a workpiece W are ground, the relative position of the grinding wheel G with respect to the workpiece W is so controlled that the reference plane RP passes the corner C between the cylindrical surface W1 and the shoulder end surface W2 of the workpiece W, as shown in FIG. 2. The grinding wheel G is then advanced toward the workpiece W in an inclined direction parallel to the reference plane RP. Accordingly, in the event that the top portion of the grinding wheel G has deviated from the reference plane RP toward the second grinding surface Gb, the shoulder end surface W2 is excessively ground when the cylindrical surface W1 is ground to a desired dimension.
Further, since the width of the second grinding surface Gb becomes smaller each time when the dressing operation is carried out, the width thereof eventually becomes smaller than that of the shoulder end surface W2. In such case, part of the shoulder end surface W2 cannot be ground by the second grinding surface Gb.